In the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Drilling rigs used in subterranean exploration must be transported to the locations where drilling activity is to be commenced. These locations are often remotely located. The transportation of such rigs on state highways requires compliance with highway safety laws and clearance underneath bridges or inside tunnels. This requirement results in extensive disassembly of full-size drilling rigs to maintain a maximum transportable width and transportable height (mast depth) with further restrictions on maximum weight, number and spacing of axles, and overall load length and turning radius. These transportation constraints vary from state to state, as well as with terrain limitations. These constraints can limit the size and capacity of rigs that can be transported and used, conflicting with the subterranean requirements to drill deeper, or longer reach horizontal wells, more quickly, requiring larger rigs.
Larger, higher capacity drilling rigs are needed for deeper (or horizontally longer) drilling operations, since the hook load for deeper operations is very high, requiring rigs to have a capacity of 500,000 lbs. and higher. Constructing longer, deeper wells requires increased torque, mud pump capacity and the use of larger diameter tubulars in longer strings. Larger equipment is required to handle these larger tubulars and longer strings. All of these considerations drive the demand for larger rigs. Larger rigs require a wider base structure for strength and wind stability, and this requirement conflicts with the transportability constraint and the time and cost of moving them. Larger rigs also require higher drill floors to accommodate taller BOP stacks. Once transported to the desired location, the large rig components must each be moved from a transport trailer into engagement with the other components located on the drilling pad. Moving a full-size rig and erecting a conventional mast and substructure generally requires the assistance of large cranes at the drilling site. The cranes will be required again when the exploration activity is complete and it is time to take the rig down and prepare it for transportation to a new drilling site.
Once the cranes have erected the mast and substructure, it is necessary to reinstall much of the machinery associated with the operation of the drilling rig. Such machinery includes, for example, the top drive with mud hose and electrical service loop, AC drawworks, rotary table, torque wrench, standpipe manifold, and BOP.
Rigs have been developed with mast raising hydraulic cylinders and with secondary substructure raising cylinders for erection of the drilling rig without the use, or with minimal use, of cranes. For example, boost cylinders have been used to fully or partially raise the substructure in combination with mast raising cylinders. These rigs have reduced rig transport and rig-up time; however, substructure hydraulics are still required and the three-step lifting process and lower mast lifting capacity remain compromised in these configurations. Also, these designs incorporate secondary lifting structures, such as mast starter legs which are separated completely from the mast for transportation. These add to rig-up and rig-down time, weight, and transportation requirements, encumber rig floor access, and may still require cranes for rig-up. Importantly, the total weight is a critical concern.
Movement of rig masts from transport trailers to engagement with substructures remains time consuming and difficult. Also, rig lifting supports create a wider mast profile, which limits the size of the structure support itself due to transportation regulations, and thus the wind load limit of the drilling rig. In particular, it is very advantageous to provide substructures having a height of less than 8 (eight) feet to minimize the incline and difficulty of moving the mast from its transport position into its connectable position on top of the collapsed substructure. However, limiting the height of the collapsed substructure restricts the overall length of retracted raising cylinders in conventional systems. It further increases the lift capacity requirement of the raising cylinder due to the disadvantageous angle created by the short distance from ground to drilling floor in the collapsed position.
For the purpose of optimizing the economics of the drilling operation, it is highly desirable to maximize the structural load capacity of the drilling rig and wind resistance without compromising the transportability of the rig, including, in particular, the width of the lower mast section, which bears the greatest load.
Assembly of drilling rigs for different depth ratings results in drilling rig designs that have different heights. Conventional systems often require the use of different raising cylinders that are incorporated in systems that are modified to accommodate the different capacity and extension requirements that are associated with drilling rigs having different heights from ground to drill floor. This increases design and construction costs, as well as the problems associated with maintaining inventories of the expensive raising cylinders in multiple sizes.
It is also highly desirable to devise a method for removing an equipment-laden lower mast section from a transport trailer into engagement with a substructure without the use of supplemental cranes. It is also desirable to minimize accessory hydraulics, and the size and number of telescopic hydraulic cylinders required for rig erection. It is also desirable to minimize accessory structure and equipment, particularly structure and equipment that may interfere with transportation or with manpower movement and access to the rig floor during drilling operations. It is also desirable to ergonomically limit the manpower interactions with rig components during rig-up for cost, safety and convenience.
It is also highly desirable to transport a drilling rig without unnecessary removal of any more drilling equipment than necessary, such as the top drive with mud hose and electrical service loop, AC drawworks, rotary table, torque wrench, standpipe manifold, and BOP. It is highly desirable to transport a drilling rig without removing the drill line normally reeved between the travelling block and the crown block. It is also highly desirable to remove the mast from the transport trailer in alignment with the substructure, and without the use of cranes. It is also desirable to maintain a low height of the collapsed substructure. It is also desirable to have a system that can adapt a single set of raising cylinders for use on substructures having different heights.
Technological and economic barriers have prevented the development of a drilling rig capable of achieving these goals. Conventional prior art drilling rig configurations remain manpower and equipment intensive to transport and rig-up. Alternative designs have failed to meet the economic and reliability requirements necessary to achieve commercial application. In particular, in deeper drilling environments, high-capacity drilling rigs are needed, such as rigs having hook loads in excess of 500,000 lbs., and with rated wind speeds in excess of 100 mph. Quick rig-down and transportation of these rigs have proven to be particularly difficult. Highway transport regulations limit the width and height of the transported mast sections as well as restricting the weight. In many states, the present width and height limit is 14 feet by 14 feet. Larger loads are subject to additional regulations including the requirement of an escort vehicle.
In summary, the preferred embodiments of the present invention provide unique solutions to many of the problems arising from a series of overlapping design constraints, including transportation limitations, rig-up limitations, hydraulic raising cylinder optimization, craneless rig-up and rig-down, and static hook load and rated wind speed requirements.